1. Field of the Invention
This invention relates to an artificial leg for assisting thigh amputees to walk, and relates in particular to an original structure for a knee joint bearing to connect the thigh and lower leg of the artificial leg.
2. Description of the Related Art
The artificial leg is an artificial limb for assisting amputees to walk, who have lost their natural leg from the thigh on downwards. In recent times, in attempts to restore to the amputee the same walking ability of physically able person, so called "intelligent artificial legs" have been proposed, housing drive mechanisms to move the lower leg in an action linked with the walking action of the thigh.
In order to provide the user of the artificial leg with as comfortable a feeling as possible, efforts were made to obtain an artificial leg with a weight equal to or within the weight of a human leg, however the intelligent leg, and in particular the mechanism housed in the lower leg portion for driving the said lower leg portion, have special characteristics which limit the extent to which the weight can be reduced, therefore making a light weight frame for the lower leg (hereafter simply referred to as the lower leg frame) necessary instead.
Therefore in the conventional art, the lower leg frame used metal materials such as aluminum alloys because of advantages such as ease of machining and high strength for achieving a lower leg frame in an artificial leg which could support the weight of the user. However, these metallic materials had the drawback of increased weight so that as one countermeasure, frames made of fiberglass providing comparatively good strength and comparatively good rigidity were commercially marketed in Europe and America.
The living habits of the user impart a large effect on the structure of the lower leg frame made of fiberglass. Design standards for strength in the artificial leg use ISO standards which in particular require as a safety margin, sufficient strength to withstand four times the weight of the user while standing. This means an exceedingly high moment acts on the knee joint bearing of the frame. However these ISO standards are based on the living habits in Europe and America where the leg is mainly used for standing and sitting in chairs, so that the main force on the lower leg frame is an axial compressive force on the lower leg frame while standing, and the moment on the knee joint bearing.
In contrast, in addition to the above, daily living in Japan, call for sitting on bent knees ("seiza") as a common part of everyday life. Therefore during this "seiza" posture (hereafter referred to as "bent knees or kneeling") an exceedingly large moment is applied in the reverse direction when standing, acting on the knee joint and the periphery of the knee joint of the lower frame. Therefore artificial leg design must also reflect the need, for handling a large moment on the knee joint bearing of the frame when the knee is bent.
More specifically, as shown in FIG. 9, this kind of artificial leg comprises a socket 21, a lower leg 23 and a foot 24. The inside of lower leg frame 25 of the lower leg 23 houses a cylinder 32 for driving the artificial leg itself, an energy source (not shown) for driving the said cylinder 32, and drive mechanisms such as valves and control equipment. The socket 21, and lower leg 23 along with a knee joint member 22 equivalent to the human knee joint, are connected for free rotating movement.
As shown in further detail in FIGS. 10 and 11, a stopper 26 for protrusion into knee joint member 22 during standing, is provided at the upper end of the lower leg frame 25 to contact a stopper 27 on the fixed side, further, a stopper 28 for protrusion into knee joint member 22 during bending, is provided at the inner wall of the lower leg frame 25 to contact a stopper 29 on the fixed side, and said stopper 29 is secured with respect to the lower leg frame 25 by means of a tightening means of machine screw and bolts (not shown) etc.
In current intelligent artificial legs, as shown in FIGS. 10(a) and 10(b), during standing of the knee joint member 22, the stopper 26 makes contact with the stopper 27 on the fixed side in the lower leg frame 25, the rotation to the front side of the socket 21 is stopped, and the standing position is maintained. When at this time, a compressive force is applied axially based on the weight of the user to the lower leg frame 25, an additional force in terms of a rotating moment M1 shown by the arrow M1 in the Figure, is applied to the vicinity of the knee joint bearing 31 of lower frame leg 25, using the fixed side stopper 27 as a support point. On the other hand, in the bent knee position in FIGS. 11(a) and 11(b), the stopper 28 makes contact with the fixed side stopper 29 installed in the lower leg frame 25, the excess rotation of the socket 21 to the floor 30 is stopped and a kneeling posture is maintained. However the load at this time on the lower leg frame 25 based on the weight of the user is applied only as rotating moment M2 along an axis 33 with the fixed side stopper 29 as a support point, and as a result, a colossal rotating moment M2 due to the weight of the user is applied in the vicinity of the knee joint bearing 31. In addition, when the artificial leg is standing, a lateral moment is applied in the vicinity of the knee joint bearing 31, in addition to the above mentioned rotating moment M1.
As can be clearly understood from FIGS. 10(a), 10(b) and FIGS. 11(a), 11(b), the rotating moment on the lower leg frame 25 acts in completely opposite directions according to the posture of the user and an exceedingly large stress is generated in the lower leg frame 25 in the vicinity of the knee joint bearing 31. Therefore the need to provide adequate strength in terms of thicker plate to support the axis 33 of said lower leg frame 25 proves unavoidable thus hindering attempts to make the lower leg frame 25 light weight.
As previously explained, the said rotating moment and the lateral moment make it necessary to support the lower leg frame of the artificial leg. However since an exceedingly large stress is generated in the support section, the thickness generally has to be altered according to the stress acting on the frame shape. When molding fiberglass parts where the thickness varies in different sections, the molding efficiency is poor because of the difficulty in obtaining a uniform injection of fiberglass. In particular, when forming protrusions and angular sections to adequately strengthen the crucial knee joint, in many cases the fiberglass does not sufficiently fill into the corners of a particular section and the part has inadequate strength to withstand the application of a high stress force. These protrusions in the inner and outer circumferential surface of the lower frame are not desirable because of bad effects on the outer appearance and since this is an artificial leg, a rather wide internal space is needed to house the drive mechanism inside the lower leg frame in order to operate the lower leg.